The findings might help explain why some people who do not get enough sleep have an increased risk for obesity, heart disease and cognitive impairment.

Sleep expert Derk-Jan Dijk and colleagues from the University of Surrey took whole-blood RNA samples from 26 participants after they had spent a week sleeping 8.5 hours a night, and the same participants after a week of sleeping for just 5.7 hours.

The expression of genes in blood offers a view into what is happening in other organs of the body, including the brain and liver, which are more difficult to test repeatedly, the authors note.

After each week, ten blood samples were taken from each participant at three-hourly intervals, during a period of total sleep deprivation that helped the researchers control the effects of light, activity and food on gene expression.

The experimental conditions mimic what many people experience on a regular basis, the researchers note in their article.

"According to the Centres for Disease Control and Prevention, 30 per cent of civilian adults in the United States report an average sleep duration of six hours or less."

Comparing the two sets of samples, the researchers found that 444 genes were down-regulated after the sleepless week, and 267 were up-regulated.

Genes related to circadian rhythms, metabolism, inflammation, immune response and stress were all affected by the experiment.

"The identified biological processes may be involved with the negative effects of sleep loss on health," the researchers say.

Window to biological mechanisms

The results "contribute to the developing evidence that poor or insufficient sleep is a health risk," comments Australian sleep researcher John Trinder from the University of Melbourne.

The new findings also open a window into the mechanisms that underpin the harmful effects of sleep deprivation, notes sleep researcher Andrew Vakulin from the Woolcock Institute of Medical Research in Sydney.

"It's a snapshot of what's going on," he says. "It's summarising what's getting turned off and on and gives us the ability to look at things much more closely now."

The new study also offers scientists avenues for studying why different individuals are more susceptible to the consequences of sleep deprivation, says Vakulin.